Neumann U87 - what FET

[Geoff Wood]

Mine has a 2N3819 in it. Probably not original. Any suggstions as to what
it should be - the Neumann schem just gives a Neumann part number ...


geoff

[Pooh Bear]

Geoff Wood wrote:

> Mine has a 2N3819 in it. Probably not original. Any suggstions as to what
> it should be - the Neumann schem just gives a Neumann part number ...

Considering the age of the U87, a 2N3819 would not surprise me if it was
original.


Graham

[Koit Saarmäe]

2SK 107

Geoff Wood wrote:

> Mine has a 2N3819 in it. Probably not original. Any suggstions as to what
> it should be - the Neumann schem just gives a Neumann part number ...
>
> geoff

[Scott Dorsey]

Geoff Wood -nospam> wrote:
>Mine has a 2N3819 in it. Probably not original. Any suggstions as to what
>it should be - the Neumann schem just gives a Neumann part number ...

That's what is in mine, and it hasn't been changed since it came from the
factory. It is almost certainly hand-selected for low noise by the Neumann
folks.

I would not be surprised if they were using a much higher grade FET today,
though.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[David Satz]

Geoff Wood wrote:

> Mine has a 2N3819 in it. Probably not original. Any suggstions
> as to what it should be - the Neumann schem just gives a Neumann
> part number ...

The more responsible microphone manufacturers select this FET quite
closely, because its function in the amplifier circuit is crucial. If
I recall correctly there is also a bias resistor whose value must be
matched to the characteristics of the particular FET that is chosen.
That's the only way to be certain of getting the low-noise performance
that your microphone is capable of. Simply swapping in a stock FET is
likely to miss the mark by several dB--definitely enough to hear in a
quiet environment, especially if yours is the older type of U 87.

I'm decent with a soldering iron, but this particular replacement is
a job that I would turn over to Neumann USA or to a well-qualified
independent shop such as Gotham Service Lab in New York. At the ultra-
high-impedance front end of the amplifier circuit, everything matters--
from the precise lead lengths to the exact position and angle in which
you mount any one component relative to the other components and the
circuit board. Stray capacitance reduces the microphone's sensitivity
and increases its distortion. A microphone's sensitivity to RFI can also
be affected greatly by small details of any work done on its front end.

So I really don't blame the manufacturer for steering you to one of
their selected FETs in place of giving a stock part number--I think it's
actually a hint to the wise, that should be taken.

However, I've owned maybe 60-80 FET-equipped microphones in 30+ years of
live recording, and have never blown a FET in any of them. It's kind of
hard to do. So I'd really wonder what caused this problem, especially
since yours seems to have blown out at least twice in this one microphone.

On the bright side--if your amplifier was previously serviced in a casual
manner, properly replacing the FET with a well-selected part and setting
the bias resistor value properly will very likely improve the sound.

[Geoff Wood]

"David Satz" > wrote in message
..
>
> However, I've owned maybe 60-80 FET-equipped microphones in 30+ years of
> live recording, and have never blown a FET in any of them. It's kind of
> hard to do. So I'd really wonder what caused this problem, especially
> since yours seems to have blown out at least twice in this one microphone.


FET not blown - just curious.

The fault was a polystyrene capacitor in the 'base-end' plastic enclosure
with a lead touching an adjacent component lead. Can't say the mic has had
a physical shock during my tenure, but one day it just wouldn't work - does
now !

It date frpm early 70's or earlier. Just called U87, and no thread on the
XLR for stand mount. satin-silver, battery board, mete, etc.


geoff